Problem: $ B = \left[\begin{array}{rrr}1 & 0 & 0 \\ 1 & 0 & 2 \\ 2 & 2 & 2\end{array}\right]$ What is $ B^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}1 & 0 & 0 \\ -\frac{1}{2} & -\frac{1}{2} & \frac{1}{2} \\ -\frac{1}{2} & \frac{1}{2} & 0\end{array}\right]$